This invention relates generally to processes for producing ceramic matrix composite (CMC) articles and articles produced thereby, and more particularly to articles form from precursor slurry compositions comprising fast curing thermosetting resins.
CMC materials generally comprise a ceramic fiber reinforcement material embedded in a ceramic matrix material. The reinforcement material serves as the load-bearing constituent of the CMC in the event of a matrix crack, while the ceramic matrix protects the reinforcement material, maintains the orientation of its fibers, and serves to dissipate loads to the reinforcement material. Of particular interest to high-temperature applications are silicon-based composites, such as silicon carbide (SiC) as the matrix and/or reinforcement material. SiC fibers have been used as a reinforcement material for a variety of ceramic matrix materials, including SiC, TiC, Si3N4, and Al2O3.
One technique for fabricating CMCs involves multiple layers of “prepreg,” often in the form of a tape-like structure, comprising the reinforcement material of the desired CMC impregnated with a precursor of the CMC matrix material. Prepregs may comprise a two-dimensional fiber array comprising a single layer of unidirectionally-aligned tows impregnated with a matrix precursor to create a generally two-dimensional laminate. Multiple plies of the resulting prepregs are stacked and debulked to form a laminate preform, a process referred to as “lay-up.” The prepregs are typically arranged so that fiber tows of the prepreg layers are oriented transverse (e.g., perpendicular) to each other, providing greater strength in the laminate plane of the preform, corresponding to the principal or load-bearing direction of the final CMC component. Following lay-up, the laminate preform will typically undergo debulking and curing while subjected to applied pressure and an elevated temperature, such as in an autoclave.
The preform may be heated in vacuum or in an inert atmosphere in order to decompose the organic binders, at least one of which pyrolizes during this heat treatment to form a carbon char, and produces a porous preform for melt infiltration. During melt infiltration, molten silicon infiltrates into the porous preform, reacts with the carbon constituent of the matrix to form silicon carbide, and fills the porosity to yield the desired CMC component.
One process is described in U.S. Pat. Nos. 5,015,540; 5,330,854; and 5,336,550. As described therein, the reinforcing fibers in the preform are coated with a low char yield slurry composition containing polymers that decompose upon heating. The polymers produce little or no char, which means that there is little or no solid material after burnout, resulting in a low strength preform. Thus there is a need for an improved preform with high strength after burn-out.
In order to address the need for a stronger and tougher preform after burnout, U.S. Pat. No. 6,258,737 describes a process for forming a CMC article using a high char yielding resin slurry composition. Although operable, this disclosed process provides an opportunity for process and product improvement, especially for reduced cycle time and minimized solvent-induced defects.